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The FDA expanded the emergency use authorizations (EUAs) for Pfizer and Moderna's COVID-19 vaccines to include booster shots for all adults, the .

Every adult who received a COVID vaccine at least 6 months prior will be eligible for a booster dose of mRNA vaccine. Previously, Pfizer and Moderna vaccine boosters were limited to those who had received a two-dose primary series at least 6 months before, and fell into specialized groups, such as adults ages 65 and up or younger adults with high-risk medical conditions or at high risk of occupational or institutional exposure to the virus. (The agency previously authorized Johnson & Johnson boosters for all recipients of that vaccine starting 2 months after the single-shot regimen.)

"Streamlining the eligibility criteria and making booster doses available to all individuals 18 years of age and older will also help to eliminate confusion about who may receive a booster dose and ensure booster doses are available to all who may need one," said Peter Marks, MD, PhD, director of FDA's Center for Biologics Evaluation and Research, in a statement.

The Pfizer booster dose is the same as the two primary shots (30 μg), while Moderna's is a half-dose (50 μg) of its primary shots.

The EUA was granted on the basis of safety and immunogenicity data provided by each manufacturer.

For Pfizer, the agency reviewed immunogenicity data from "approximately 200 participants" ages 18-55. Interestingly, FDA made no mention of data released from Pfizer's randomized booster trial of over 10,000 individuals ages 16 and up. The phase III trial found that the booster dose was safe and demonstrated a relative 95.6% efficacy versus those who had only received a two-dose primary series.

Moderna's EUA was granted on the basis of immunogenicity data from 149 adults from P201, a phase II trial, who received the two-dose 100 μg series (the dose authorized under EUA) plus the booster dose, which FDA said "demonstrated a booster response."

FDA's Vaccines and Related Biological Products Advisory Committee (VRBPAC) had previously discussed these immunogenicity data back in September (Pfizer) and October (Moderna) prior to the authorizations for high-risk populations. But there was no VRBPAC meeting to discuss this EUA. Previously, the agency's advisors had shown no appetite for boosters in all adults, voting against Pfizer's initial application by a vote of 16-2 and not wanting to discuss it during Moderna's review.

In Friday's announcement, FDA noted the increased risk of vaccine-associated myocarditis and pericarditis, but determined that "the benefits of a single booster dose [...] outweigh the risks" in adults ages 18 and up.

The CDC's Advisory Committee on Immunization Practices will meet later on Friday to discuss recommendations for boosters.

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